Hydroxyl Polymer Fiber Fibrous Structures and Processes for Making Same

ABSTRACT

Hydroxyl polymer fiber fibrous structures and processes for making same are provided. More particularly, hydroxyl polymer fiber fibrous structures comprising a non-naturally occurring hydroxyl polymer fiber wherein the fibrous structure exhibits a total pore volume of pores in the range of greater than 20 μm to 500 μm of greater than 3.75 mm 3 /mg of dry fibrous structure mass, and/or fibrous structures comprising a hydroxyl polymer fiber and a solid additive are provided.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/504,899, which claims the benefit of U.S. Provisional Application No.60/710,109 filed on Aug. 22, 2005.

FIELD OF THE INVENTION

The present invention relates to hydroxyl polymer fiber fibrousstructures and processes for making same. More particularly, the presentinvention relates to hydroxyl polymer fiber fibrous structurescomprising a non-naturally occurring hydroxyl polymer fiber wherein thefibrous structure exhibits a total pore volume of pores in the range ofgreater than 20 μm to 500 μm of greater than 3.75 mm³/mg dry fibrousstructure mass, as determined by the Pore Volume Distribution TestMethod, described herein, and/or fibrous structures comprising ahydroxyl polymer fiber and a solid additive.

BACKGROUND OF THE INVENTION

Hydroxyl polymer fiber fibrous structures are known in the art. However,such fibrous structures have a tendency to collapse (i.e., decrease incaliper in the z-direction, which is perpendicular to the planarsurfaces of the fibrous structures) (and definitely not “grow”; i.e.,increase in caliper in the z-direction) when subjected to a liquid, suchas water.

Accordingly, there is a need for hydroxyl polymer fiber fibrousstructures that avoid or reduce such a collapse when subjected to aliquid, and process for making same.

SUMMARY OF THE INVENTION

The present invention fulfills the need described above by providinghydroxyl polymer fiber fibrous structures that avoid or reduce collapseof the fibrous structure and/or that grow or have one or more portionsthat grow when the fibrous structure is subjected to a liquid, andprocesses for making same.

In one example of the present invention, a fibrous structure comprisinga plurality of non-naturally occurring polysaccharide fibers and aplurality of solid additives, is provided. In one example, such afibrous structure exhibits a total pore volume of pores in the range ofgreater than 20 μm to 500 μm of greater than 3.75 and/or greater than3.81 and/or greater than 3.87 and/or greater than 3.90 and/or greaterthan 3.96 and/or greater than 4.00 mm³/mg dry fibrous structure mass, asdetermined by the Pore Volume Distribution Test Method, describedherein.

In another example of the present invention, a fibrous structurecomprising a non-naturally occurring hydroxyl polymer fiber wherein thefibrous structure exhibits a total pore volume of pores in the range ofgreater than 20 μm to 500 μm of greater than 3.75 and/or greater than3.81 and/or greater than 3.87 and/or greater than 3.90 and/or greaterthan 3.96 and/or greater than 4.00 mm³/mg dry fibrous structure mass, asdetermined by the Pore Volume Distribution Test Method, describedherein, is provided.

In another example of the present invention, a fibrous structurecomprising a non-naturally occurring hydroxyl polymer fiber and a solidadditive, is provided.

In still another example of the present invention, a single- ormulti-ply sanitary tissue product comprising a fibrous structureaccording to the present invention is provided.

In yet another example of the present invention, a process for making afibrous structure, the process comprising the steps of:

a. providing a fibrous structure comprising a plurality of non-naturallyoccurring hydroxyl polymer fibers; and

b. contacting a surface of the fibrous structure with a plurality ofsolid additives such that the solid additives cover less than the entiresurface area of the surface of the fibrous structure, is provided.

In even yet another example of the present invention, a process formaking a fibrous structure, the process comprising the steps of:

a. providing a first gas stream comprising a plurality of non-naturallyoccurring hydroxyl polymer fibers;

b. providing a second gas stream comprising a plurality of solidadditives; and

c. collecting the non-naturally occurring hydroxyl polymer fibers andthe solid additives on a collection device such that a fibrous structureis formed, is provided.

In still yet another example of the present invention, a fibrousstructure comprising non-naturally occurring hydroxyl polymer fibers andsolid additives, wherein the non-naturally occurring hydroxyl polymerfibers are present in the fibrous structure at a greater bone dry weightthan the solid additives, is provided.

In even still another example of the present invention, a fibrousstructure comprising a plurality of non-naturally occurring hydroxylpolymer fibers and a pore volume enhancing system that increases thetotal pore volume per dry fibrous structure mass of pores in the rangeof greater than 20 μm to 500 μm of the fibrous structure compared to thesame fibrous structure without the pore volume enhancing system. In oneexample, the pore volume enhancing system may comprise a solid additive.

In even still yet another example of the present invention, a fibrousstructure comprising a plurality of non-naturally occurring hydroxylpolymer fibers wherein at least a portion of the fibrous structureremains elevated above another portion of the fibrous structure afterboth portions have been subjected to a liquid, such as an aqueous liquid(for example water).

In still yet another example of the present invention, a fibrousstructure comprising a plurality of non-naturally occurring hydroxylpolymer fibers wherein at least a portion of the fibrous structureexhibits a height after being subjected to a liquid, such as an aqueousliquid (for example water), that is greater than its height prior tobeing subjected to a liquid, such as an aqueous liquid (for examplewater).

Accordingly, the present invention provides fibrous structurescomprising a non-naturally occurring hydroxyl polymer fiber wherein thefibrous structure exhibits a total pore volume of pores in the range ofgreater than 20 μm to 500 μm of greater than 3.75 mm³/mg dry fibrousstructure mass, as determined by the Pore Volume Distribution TestMethod, described herein, fibrous structures comprising a non-naturallyoccurring hydroxyl polymer fiber and a solid additive, fibrousstructures comprising a pore volume enhancing system, sanitary tissueproducts comprising such fibrous structures and processes for makingsuch fibrous structures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic representation of a side view of a barrel of atwin screw extruder suitable for use in the present invention.

FIG. 1B is a schematic side view of a screw and mixing elementconfiguration suitable for use in the barrel of FIG. 1A.

FIG. 2 is a schematic perspective representation of one example of afibrous structure according to the present invention;

FIG. 3 is a cross-sectional view of the fibrous structure of FIG. 2taken along line 3-3;

FIG. 4 is a schematic perspective representation of one of example of amulti-layered fibrous structure according to the present invention witha partial cut-away to expose the layers;

FIG. 5 is a cross-sectional view of the multi-layered fibrous structureof FIG. 4 taken along line 5-5;

FIG. 6 is a schematic perspective representation of another example of afibrous structure according to the present invention; and

FIG. 7 is a schematic perspective representation of another example of afibrous structure according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION Definitions

“Non-naturally occurring” as used herein with respect to “non-naturallyoccurring hydroxyl polymer fibers” and/or “non-naturally occurringmaterials” means that the hydroxyl polymer fibers and/or materials arenot found in nature in that form. In other words, some chemicalprocessing of materials needs to occur in order to obtain thenon-naturally occurring hydroxyl polymer fibers and/or non-naturallyoccurring materials. For example, wood pulp fiber is a naturallyoccurring hydroxyl polymer fiber, however, if the wood pulp fiber ischemically processed, such as via a lyocell-type process, a solution ofhydroxyl polymer is formed. The solution of hydroxyl polymer may then bespun into a fiber. Accordingly, this fiber is considered to be anon-naturally occurring hydroxyl polymer fiber since it is not directlyobtainable from nature in its present form.

“Naturally occurring” as used herein means that a material is found innature in its present form. An example of a naturally occurring materialis a wood pulp fiber.

A “fibrous structure” as used herein means a single web structure thatcomprises at least one fiber. For example, a fibrous structure of thepresent invention may comprise one or more fibers, wherein at least oneof the fibers comprises a hydroxyl polymer fiber.

In another example, a fibrous structure of the present invention maycomprise a plurality of fibers, wherein at least one (sometimes amajority, even all) of the fibers comprises a hydroxyl polymer fiber.The fibrous structures of the present invention may be layered such thatone layer of the fibrous structure may comprise a different compositionof fibers and/or materials from another layer of the same fibrousstructure.

“Surface of a fibrous structure” as used herein means that portion of afibrous structure that is exposed to the external environment. In otherwords, the surface of a fibrous structure is that portion of the fibrousstructure that is not completely surrounded by other portions of thefibrous structure.

“Hydroxyl polymer” as used herein includes any hydroxyl-containingpolymer that can be incorporated into a fibrous structure of the presentinvention, such as into a fibrous structure in the form of a fiber.

In one example, the hydroxyl polymer of the present invention includesgreater than 10% and/or greater than 20% and/or greater than 25% byweight hydroxyl moieties.

Nonlimiting examples of hydroxyl polymers in accordance with the presentinvention include polyols, such as polyvinyl alcohol, polyvinyl alcoholderivatives, polyvinyl alcohol copolymers, starch, starch derivatives,starch copolymers, chitosan, chitosan derivatives, chitosan copolymers,cellulose, cellulose derivatives such as cellulose ether and esterderivatives, cellulose copolymers, gums, arabinans, galactans, proteinsand various other polysaccharides and mixtures thereof.

Classes of hydroxyl polymers are defined by the hydroxyl polymerbackbone. For example polyvinyl alcohol and polyvinyl alcoholderivatives and polyvinyl alcohol copolymers are in the class ofpolyvinyl alcohol hydroxyl polymers whereas starch and starchderivatives are in the class of starch hydroxyl polymers.

The hydroxyl polymer may have a weight average molecular weight of fromabout 10,000 to about 40,000,000 g/mol. Higher and lower molecularweight hydroxyl polymers may be used in combination with hydroxylpolymers having the exemplified weight average molecular weight.

Well known modifications of hydroxyl polymer, such as natural starches,include chemical modifications and/or enzymatic modifications. Forexample, the natural starch can be acid-thinned, hydroxy-ethylated,hydroxy-propylated, and/or oxidized. In addition, the hydroxyl polymermay comprise dent corn starch hydroxyl polymer.

Polyvinyl alcohols herein can be grafted with other monomers to modifyits properties. A wide range of monomers has been successfully graftedto polyvinyl alcohol. Nonlimiting examples of such monomers includevinyl acetate, styrene, acrylamide, acrylic acid, 2-hydroxyethylmethacrylate, acrylonitrile, 1,3-butadiene, methyl methacrylate,methacrylic acid, vinylidene chloride, vinyl chloride, vinyl amine and avariety of acrylate esters.

“Polysaccharides” as used herein means natural polysaccharides andpolysaccharide derivatives or modified polysaccharides. Suitablepolysaccharides include, but are not limited to, starches, starchderivatives, chitosan, chitosan derivatives, cellulose derivatives,gums, arabinans, galactans and mixtures thereof.

“Fiber” as used herein means a slender, thin, and highly flexible objecthaving a major axis which is very long, compared to the fiber's twomutually-orthogonal axes that are perpendicular to the major axis. Inone example, an aspect ratio of the major's axis length to an equivalentdiameter of the fiber's cross-section perpendicular to the major axis isgreater than 100/1, more specifically greater than 500/1, and still morespecifically greater than 1000/1, and even more specifically, greaterthan 5000/1.

The fibers of the present invention may be continuous or substantiallycontinuous. A fiber is continuous if it extends 100% of the MD length ofthe fibrous structure and/or fibrous structure and/or sanitary tissueproduct made therefrom. In one example, a fiber is substantiallycontinuous if it extends greater than about 30% and/or greater thanabout 50% and/or greater than about 70% of the MD length of the fibrousstructure and/or sanitary tissue product made therefrom. In anotherexample, continuous or substantially continuous fiber in accordance withthe present invention may exhibit a length of greater than 3.81 cm (1.5inches).

The fiber can have a fiber diameter as determined by the Fiber DiameterTest Method described herein of less than about 50 microns and/or lessthan about 20 microns and/or less than about 10 microns and/or less thanabout 8 microns and/or less than about 6 microns.

The fibers may include melt spun fibers, dry spun fibers and/or spunbondfibers, staple fibers, hollow fibers, shaped fibers, such as multi-lobalfibers and multicomponent fibers, especially bicomponent fibers. Themulticomponent fibers, especially bicomponent fibers, may be in aside-by-side, sheath-core, segmented pie, ribbon, islands-in-the-seaconfiguration, or any combination thereof. The sheath may be continuousor non-continuous around the core. The ratio of the weight of the sheathto the core can be from about 5:95 to about 95:5. The fibers of thepresent invention may have different geometries that include round,elliptical, star shaped, rectangular, trilobal and other variouseccentricities.

“Sanitary tissue product” as used includes but is not limited to awiping implement for post-urinary and post-bowel movement cleaning(toilet tissue), for otorhinolaryngological discharges (facial tissue),and multi-functional absorbent, cleaning uses (absorbent towels), wipes,feminine care products and diapers.

A sanitary tissue product of the present invention comprises at leastone fibrous structure in accordance with the present invention. In oneexample, a fibrous structure and/or sanitary tissue product according tothe present invention exhibits an initial total wet tensile of at leastabout 8 g/2.54 cm (8 g/in) and/or at least about 10 g/2.54 cm (10 g/in)and/or at least about 15 g/2.54 cm (15 g/in) and/or at least about 20g/2.54 cm (20 g/in) and/or at least about 40 g/2.54 cm (40 g/in).

In another example, a fibrous structure and/or a sanitary tissue productof the present invention exhibits an initial total wet tensile, asmeasured by the Initial Total Wet Tensile Test Method described herein,of less than about 500 g/2.54 cm (500 g/in) and/or less than about 400g/2.54 cm (400 g/in) and/or less than about 300 g/2.54 cm (300 g/in)and/or less than about 200 g/2.54 cm (200 g/in) and/or less than about150 g/2.54 cm (150 g/in) and/or less than about 120 g/2.54 cm (120 g/in)and/or less than about 100 g/2.54 cm (100 g/in).

In yet another example, a fibrous structure and/or a sanitary tissueproduct of the present invention may exhibit an initial total wettensile of from about 8 g/2.54 cm (8 g/in) to about 500 g/2.54 cm (500g/in) and/or from about 40 g/2.54 cm (40 g/in) to about 500 g/2.54 cm(500 g/in) and/or from about 60 g/2.54 cm (60 g/in) to about 500 g/2.54cm (500 g/in) and/or from about 65 g/2.54 cm (65 g/in) to about 450g/2.54 cm (450 g/in) and/or from about 70 g/2.54 cm (70 g/in) to about400 g/2.54 cm (400 g/in) and/or from about 75 g/2.54 cm (75 g/in) toabout 400 g/2.54 cm (400 g/in) and/or from about 80 g/2.54 cm (80 g/in)to about 300 g/2.54 cm (300 g/in) and/or from about 80 g/2.54 cm (80g/in) to about 200 g/2.54 cm (200 g/in) and/or from about 80 g/2.54 cm(80 g/in) to about 150 g/2.54 cm (150 g/in) and/or from about 80 g/2.54cm (80 g/in) to about 120 g/2.54 cm (120 g/in) and/or from about 80g/2.54 cm (80 g/in) to about 100 g/2.54 cm (100 g/in).

In one example, a fibrous structure and/or a sanitary tissue productaccording to the present invention exhibits a minimum total dry tensileof at least about 70 g/2.54 cm (70 g/in) and/or at least about 100g/2.54 cm (100 g/in) and/or at least about 300 g/2.54 cm (300 g/in)and/or at least about 500 g/2.54 cm (500 g/in) and/or at least about 700g/2.54 cm (700 g/in) and/or at least about 800 g/2.54 cm (800 g/in)and/or at least about 900 g/2.54 cm (900 g/in) and/or at least about1000 g/2.54 cm (1000 g/in).

In another example, a fibrous structure and/or a sanitary tissue productaccording to the present invention exhibits a maximum total dry tensileof less than about 5000 g/2.54 cm (5000 g/in) and/or less than about4000 g/2.54 cm (4000 g/in) and/or less than about 2000 g/2.54 cm (2000g/in) and/or less than about 1700 g/2.54 cm (1700 g/in) and/or less thanabout 1500 g/2.54 cm (1500 g/in).

In even another example, a fibrous structure and/or a sanitary tissueproduct according to the present invention exhibits a wet lint score ofless than about 25 and/or less than 20 and/or less than 15 and/or lessthan 10.

In yet another example, a sanitary tissue product according to thepresent invention exhibits a total dry tensile within a range of aminimum and maximum total dry tensile value as described above.

In still yet another example, a fibrous structure and/or a sanitarytissue product according to the present invention exhibits a Dry LintScore of less than about 10 and/or less than about 8 and/or less thanabout 7 and/or less than about 6 and/or less than about 5.5.

In addition to sanitary tissue products, the fibrous structures of thepresent invention may be utilized in any number of various otherapplications known in the art. For example, in some examples, thefibrous structures may be utilized as packaging materials, wounddressings, etc.

“Ply” or “Plies” as used herein means a single fibrous structureoptionally to be disposed in a substantially contiguous, face-to-facerelationship with other plies, forming a multi-ply sanitary tissueproduct. It is also contemplated that a single fibrous structure caneffectively form two “plies” or multiple “plies”, for example, by beingfolded on itself. Ply or plies can also exist as films.

One or more layers may be present in a single ply. For example, two ormore layers of different compositions may form a single ply. In otherwords, the two or more layers are substantially or completely incapableof being physically separated from each other without substantiallydamaging the ply.

“Weight average molecular weight” as used herein means the weightaverage molecular weight as determined using gel permeationchromatography according to the protocol found in Colloids and SurfacesA. Physico Chemical & Engineering Aspects, Vol. 162, 2000, pg. 107-121.

“Caliper” as used herein means the macroscopic thickness of a sample.Caliper of a sample of fibrous structure according to the presentinvention is determined by cutting a sample of the fibrous structuresuch that it is larger in size than a load foot loading surface wherethe load foot loading surface has a circular surface area of about 3.14in². The sample is confined between a horizontal flat surface and theload foot loading surface. The load foot loading surface applies aconfining pressure to the sample of 15.5 g/cm² (about 0.21 psi). Thecaliper is the resulting gap between the flat surface and the load footloading surface. Such measurements can be obtained on a VIR ElectronicThickness Tester Model II available from Thwing-Albert InstrumentCompany, Philadelphia, Pa. The caliper measurement is repeated andrecorded at least five (5) times so that an average caliper can becalculated.

“Additive” as used herein means a material that is present in and/or ona fibrous structure at low levels. For example, an additive is amaterial that is present in and/or on a fibrous structure at levels lessthan 50% and/or less than 45% and/or less than 40% and/or less than 30%and/or less than 20% and/or less than 10% and/or less than 5% and/orless than 3% and/or less than 1% and/or less than 0.5% to about 0% byweight of the fibrous structure.

“Solid additive” as used herein means an additive that is capable ofbeing applied to a surface of a fibrous structure in a solid form. Inother words, the solid additive of the present invention can bedelivered directly to a surface of a fibrous structure without a liquidphase being present, i.e. without melting the solid additive and withoutsuspending the solid additive in a liquid vehicle or carrier. As such,the solid additive of the present invention does not require a liquidstate or a liquid vehicle or carrier in order to be delivered to asurface of a fibrous structure. The solid additive or the presentinvention may be delivered via a gas or combinations of gases. Forpurposes of the present invention, delivery of an additive, liquidand/or solid, into a slurry of fibers used to produce a fibrousstructure is not encompassed by this phrase. However, such an additivemay be present in a finished fibrous structure so long as the finishedfibrous structure also comprises a solid additive as defined herein.Further, an additive, liquid and/or solid, delivered to a fibrousstructure via a liquid vehicle, such as a latex emulsion, may be presentin a finished fibrous structure so long as the finished fibrousstructure also comprises a solid additive as defined herein. Further, anadditive, liquid and/or solid, delivered to a fibrous structure viamelting, such as a hot melt adhesive, may be present in a finishedfibrous structure so long as the finished fibrous structure alsocomprises a solid additive as defined herein. In one example, insimplistic terms, a solid additive is an additive that when placedwithin a container, does not take the shape of the container.

Nonlimiting examples of suitable solid additives include hydrophilicinorganic particles, hydrophilic organic particles, hydrophobicinorganic particles, hydrophobic organic particles, naturally occurringfibers, non-naturally occurring particles and other non-naturallyoccurring fibers.

In one example, the naturally occurring fibers may comprise wood pulpfibers, trichomes, seed hairs, protein fibers, such as silk and/or wool,and/or a cotton linters.

In another example, the other non-naturally occurring fibers maycomprise polyolefin fibers and/or polyamide fibers.

In another example, the hydrophilic inorganic particles are selectedfrom the group consisting of: clay, calcium carbonate, titanium dioxide,talc, aluminum silicate, calcium silicate, alumina trihydrate, activatedcarbon, calcium sulfate, glass microspheres, diatomaceous earth andmixtures thereof.

In one example, hydrophilic organic particles of the present inventionmay include hydrophobic particles the surfaces of which have beentreated by a hydrophilic material. A description of a suitable processfor surface treating a hydrophobic material with a hydrophilic materialis described in U.S. Pat. No. 4,139,660. Nonlimiting examples of suchhydrophilic organic particles include polyesters, such as polyethyleneterephthalate particles that have been surface treated with a soilrelease polymer and/or surfactant. Another example is a polyolefinparticle that has been surface treated with a surfactant.

In another example, the hydrophilic organic particles may compriseabsorbent gel materials (AGM) such as hydrogels, superabsorbentmaterials, hydrocolloidal materials and mixtures thereof. In oneexample, the hydrophilic organic particle comprises polyacrylate. Othernonlimiting examples of suitable hydrophilic organic particles are knownin the art. For example, U.S. Pat. No. 5,428,076 describes numerousexamples of hydrophilic organic particles that are suitable for thepresent invention.

In another example, the hydrophilic organic particles may comprise highmolecular weight starch particles (high amylose-containing starchparticles), such as Hylon 7 available from National Starch.

In another example, the hydrophilic organic particles may comprisecellulose particles.

In another example, the hydrophilic organic particles may comprisecompressed cellulose sponge particles. Fibrous structures comprisingcompressed cellulose sponge particles may expand more than 2 timesand/or more than 3 times and/or more than 4 times their original stateafter being contacted by a liquid, such as an aqueous liquid (forexample water).

In one example of a solid additive in accordance with the presentinvention, the solid additive exhibits a surface tension of greater thanabout 30 and/or greater than about 35 and/or greater than about 40and/or greater than about 50 and/or greater than about 60 dynes/cm asdetermined by ASTM D2578.

The solid additives of the present invention may have differentgeometries and/or cross-sectional areas that include round, elliptical,star-shaped, rectangular, trilobal and other various eccentricities.

In one example, the solid additive may exhibit a particle size of lessthan 6 mm and/or less than 5.5 mm and/or less than 5 mm and/or less than4.5 mm and/or less than 4 mm and/or less than 2 mm in its maximumdimension.

“Particle” as used herein means an object having an aspect ratio of lessthan about 25/1 and/or less than about 15/1 and/or less than about 10/1and/or less than 5/1 to about 1/1. A particle is not a fiber as definedherein.

Hydroxyl Polymer Fiber

The hydroxyl polymer fiber of the present invention may comprise one ormore polymers. In one example, the hydroxyl polymer fiber comprises afirst polymer and a second polymer, wherein one of the two polymers isinherently thermoplastic and thus, melts and/or flows without the needof a plasticizer when subjected to a temperature above its Tg. The otherpolymer may require a plasticizer, such as water, sorbitol, glycerine,polyols, such as polyethylene glycols, ethylene glycol, polyethyleneglycol, urea, sucrose, and esters, and combinations thereof to permit itto melt and/or flow when subjected to a temperature above its Tg (i.e.,a thermoplasticizable polymer). In one example, the first polymer andthe second polymer are hydroxyl polymers. In another example, the firstpolymer and the second polymer are different classes of hydroxylpolymers, such as starch hydroxyl polymer and polyvinyl alcohol hydroxylpolymer. The polymers of the hydroxyl polymer fiber may be crosslinkablevia a crosslinking system to themselves and/or to the each other.

The hydroxyl polymer fiber of the present invention can be produced bypolymer processing, for example meltblowing, spunbonding, and/or rotaryspinning, a polymer composition.

Polymer Composition

The polymer composition of the present invention may have a shearviscosity of from about 1 Pascal·Seconds to about 25 Pascal·Secondsand/or from about 2 Pascal·Seconds to about 20 Pascal·Seconds and/orfrom about 3 Pascal·Seconds to about 10 Pascal·Seconds, as measured at ashear rate of 3,000 sec⁻¹ and at the processing temperature (50° C. to100° C.).

The polymer composition may have a temperature of from about 50° C. toabout 100° C. and/or from about 65° C. to about 95° C. and/or from about70° C. to about 90° C. when making fibers from the polymer composition.

The pH of the polymer composition may be from about 2.5 to about 9and/or from about 3 to about 8.5 and/or from about 3.2 to about 8 and/orfrom about 3.2 to about 7.5.

In one example, a polymer composition of the present invention maycomprise from about 30% and/or 40% and/or 45% and/or 50% to about 75%and/or 80% and/or 85% and/or 90% and/or 95% and/or 99.5% by weight ofthe polymer composition of a hydroxyl polymer. The hydroxyl polymer mayhave a weight average molecular weight greater than about 100,000 g/molprior to crosslinking.

The polymer composition may exhibit a Capillary Number of at least 1and/or at least 3 and/or at least 5 such that the polymer compositioncan be effectively polymer processed into a hydroxyl polymer fiber.

The Capillary number is a dimensionless number used to characterize thelikelihood of this droplet breakup. A larger capillary number indicatesgreater fluid stability upon exiting the die. The Capillary number isdefined as follows:

${Ca} = \frac{V*\eta}{\sigma}$

V is the fluid velocity at the die exit (units of Length per Time),η is the fluid viscosity at the conditions of the die (units of Mass perLength*Time),σ is the surface tension of the fluid (units of mass per Time²). Whenvelocity, viscosity, and surface tension are expressed in a set ofconsistent units, the resulting Capillary number will have no units ofits own; the individual units will cancel out.

The Capillary number is defined for the conditions at the exit of thedie. The fluid velocity is the average velocity of the fluid passingthrough the die opening. The average velocity is defined as follows:

$V = \frac{{Vol}^{\prime}}{Area}$

Vol′=volumetric flowrate (units of Length³ per Time),Area=cross-sectional area of the die exit (units of Length).

When the die opening is a circular hole, then the fluid velocity can bedefined as

$V = \frac{{Vol}^{\prime}}{\pi*R^{2}}$

R is the radius of the circular hole (units of length).

The fluid viscosity will depend on the temperature and may depend of theshear rate. The definition of a shear thinning fluid includes adependence on the shear rate. The surface tension will depend on themakeup of the fluid and the temperature of the fluid.

In a fiber spinning process, the filaments need to have initialstability as they leave the die. The Capillary number is used tocharacterize this initial stability criterion. At the conditions of thedie, the Capillary number should be greater than 1 and/or greater than4.

In one example, the polymer composition exhibits a Capillary Number offrom at least 1 to about 50 and/or at least 3 to about 50 and/or atleast 5 to about 30. Further, the polymer composition may exhibit a pHof from at least about 4 to about 12 and/or from at least about 4.5 toabout 11.5 and/or from at least about 4.5 to about 11.

A crosslinking system comprising a crosslinking agent may be present inthe polymer composition and/or may be added to the polymer compositionbefore polymer processing of the polymer composition. Further, acrosslinking system may be added to the hydroxyl polymer fiber afterpolymer processing the polymer composition. “Crosslinking agent” as usedherein means any material that is capable of crosslinking a hydroxylpolymer within a polymer composition according to the present.

Nonlimiting examples of suitable crosslinking agents includepolycarboxylic acids, imidazolidinones and other compounds resultingfrom alkyl substituted or unsubstituted cyclic adducts of glyoxal withureas, thioureas, guanidines, methylene diamides, and methylenedicarbamates and derivatives thereof; and mixtures thereof.

Upon crosslinking the hydroxyl polymer, the crosslinking agent becomesan integral part of the hydroxyl polymer fiber as a result ofcrosslinking the hydroxyl polymer as shown in the following schematicrepresentation:

Hydroxyl polymer—Crosslinking agent—Hydroxyl polymer

In another example, the crosslinking system of the present invention maybe applied to a pre-existing hydroxyl polymer fiber as a coating and/orsurface treatment.

The polymer composition may comprise a) from about 30% and/or 40% and/or45% and/or 50% to about 75% and/or 80% and/or 85% and/or 90% and/or99.5% by weight of the polymer composition of one or more hydroxylpolymers; b) a crosslinking system comprising from about 0.1% to about10% by weight of the polymer composition of a crosslinking agent; and c)from about 0% and/or 10% and/or 15% and/or 20% to about 50% and/or 55%and/or 60% and/or 70% by weight of the polymer composition of anexternal plasticizer e.g., water.

The polymer composition may comprise two or more different classes ofhydroxyl polymers at weight ratios of from about 20:1 and/or from about15:1 and/or from about 10:1 and/or from about 5:1 and/or from about 2:1and/or from about 1:1 to about 1:20 and/or to about 1:15 and/or to about1:10 and/or to about 1:5 and/or to about 1:2 and/or to about 1:1.

In one example, the polymer composition comprises from about 0.01% toabout 20% and/or from about 0.1% to about 15% and/or from about 1% toabout 12% and/or from about 2% to about 10% by weight of a first classof hydroxyl polymer, such as a polyvinyl alcohol hydroxyl polymer andfrom about 20% to about 99.99% and/or from about 25% to about 95% and/orfrom about 30% to about 90% and/or from about 40% to about 70% by weightof a second class of hydroxyl polymer, such as a starch hydroxylpolymer.

Process for Making a Hydroxyl Polymer Fiber Fibrous Structure

Any suitable process known to those skilled in the art can be used toproduce the polymer composition and/or to polymer process the polymercomposition and/or to produce the hydroxyl polymer fiber of the presentinvention. Nonlimiting examples of such processes are described inpublished applications: EP 1 035 239, EP 1 132 427, EP 1 217 106, EP 1217 107, WO 03/066942 and U.S. Pat. No. 5,342,225.

a. Making a Polymer Composition

In one example, a polymer composition according to the presentinvention, comprises a first class of polymers and a second class ofpolymers. The first class of polymers, which in this example comprisesabout 50:50 dry weight ratio of two different starches, comprises anacid thinned dent corn starch hydroxyl polymer (for example Eclipse®G—commercially available from A.E. Staley) and an ethoxylated cornstarch hydroxyl polymer (for example Ethylex® 2035—commerciallyavailable from A.E. Staley) and the second class of polymers comprises apolyvinyl alcohol hydroxyl polymer (for example Celvol® 310—commerciallyavailable from Celanese). In addition to the hydroxyl polymers, thepolymer composition comprises an alkaline agent, (for example sodiumhydroxide), a cationic agent (for example Arquad® 12-37—commerciallyavailable from Akzo Nobel), a crosslinking system comprising acrosslinking agent as described herein, and a crosslinking facilitator(for example ammonium chloride). Further, the polymer compositioncomprises a plasticizer (for example water). A sufficient amount ofwater is added the polymer composition such that the polymer compositionexhibits a Capillary Number of at least 1.

A polymer composition of the present invention may be prepared using ascrew extruder, such as a vented twin screw extruder.

A barrel 10 of an APV Baker (Peterborough, England) twin screw extruderis schematically illustrated in FIG. 1A. The barrel 10 is separated intoeight zones, identified as zones 1-8. The barrel 10 encloses theextrusion screw and mixing elements, schematically shown in FIG. 1B, andserves as a containment vessel during the extrusion process. A solidfeed port 12 is disposed in zone 1 and a liquid feed port 14 is disposedin zone 1. A vent 16 is included in zone 7 for cooling and decreasingthe liquid, such as water, content of the mixture prior to exiting theextruder. An optional vent stuffer, commercially available from APVBaker, can be employed to prevent the polymer composition from exitingthrough the vent 16. The flow of the polymer composition through thebarrel 10 is from zone 1 exiting the barrel 10 at zone 8.

A screw and mixing element configuration for the twin screw extruder isschematically illustrated in FIG. 1B. The twin screw extruder comprisesa plurality of twin lead screws (TLS) (designated A and B) and singlelead screws (SLS) (designated C and D) installed in series. Screwelements (A-D) are characterized by the number of continuous leads andthe pitch of these leads.

A lead is a flight (at a given helix angle) that wraps the core of thescrew element. The number of leads indicates the number of flightswrapping the core at any given location along the length of the screw.Increasing the number of leads reduces the volumetric capacity of thescrew and increases the pressure generating capability of the screw.

The pitch of the screw is the distance needed for a flight to completeone revolution of the core. It is expressed as the number of screwelement diameters per one complete revolution of a flight. Decreasingthe pitch of the screw increases the pressure generated by the screw anddecreases the volumetric capacity of the screw.

The length of a screw element is reported as the ratio of length of theelement divided by the diameter of the element.

This example uses TLS and SLS. Screw element A is a TLS with a 1.0 pitchand a 1.5 length ratio. Screw element B is a TLS with a 1.0 pitch and a1.0 L/D ratio. Screw element C is a SLS with a ¼ pitch and a 1.0 lengthratio. Screw element D is a SLS and a ¼ pitch and a ½ length ratio.

Bilobal paddles, E, serving as mixing elements, are also included inseries with the SLS and TLS screw elements in order to enhance mixing.Various configurations of bilobal paddles and reversing elements F,single and twin lead screws threaded in the opposite direction, are usedin order to control flow and corresponding mixing time.

In zone 1, a first hydroxyl polymer (for example dent corn starch)and/or first hydroxyl polymer composition (for example dent corn starchand an ethoxylated starch) is fed into the solid feed port at a rate of183 grams/minute using a K-Tron (Pitman, N.J.) loss-in-weight feeder. Asecond hydroxyl polymer and/or second hydroxyl polymer composition isfed into the same port via a second K-tron feeder at a rate of 38grams/minute.

Optionally the second hydroxyl polymer and/or second hydroxyl polymercomposition may be prepared separately and added as a water-basedpolymer composition according to the following procedure. The secondhydroxyl polymer and/or second hydroxyl polymer composition is preparedin a scraped wall reaction vessel (Chemplant Stainless Holdings Ltd.Dalton, England). The reaction vessel is capable of heating through anoil jacket and may be pressurized to prevent water loss at elevatedtemperatures. Water, an external plasticizer, is introduced into thevessel and while stirring the second hydroxyl polymer (for examplepolyvinyl alcohol) is added, optionally another hydroxyl polymer (forexample an ethoxylated starch) may also be added during this step.Additional components such as surfactants or alkaline materials such assodium/ammonium hydroxide may be added. The additive port of thereaction vessel is then closed, sealed and pressurized to 20 psi. Thereaction vessel is then heated to about 110° C. while stirring forapproximately one hour and then is pressure fed through supply lines toa B9000 pump for metered feeding into the zone 1 of the extruder, aspreviously described. Adjustments are made to the feed rates to keep thetotal polymer addition to about 220 grams/minute and the water to about136 grams/minute.

The first hydroxyl polymer and/or first hydroxyl polymer composition andthe second hydroxyl polymer and/or second hydroxyl polymer compositionare combined inside the extruder (zone 1) with the water, an externalplasticizer, added at the liquid feed at a rate of 136 grams/minuteusing a Milton Roy (Ivyland, Pa.) diaphragm pump (1.9 gallon per hourpump head) to form a third hydroxyl polymer composition. The thirdhydroxyl polymer composition is then conveyed down the barrel of theextruder and cooked, in the presence of an alkaline agent, such asammonium hydroxide and/or sodium hydroxide. (introduction of externalplasticizer such as glycerin) The cooking causes a hydrogen from atleast one hydroxyl moiety on one or more of the hydroxyl polymers tobecome disassociated from the oxygen atom of the hydroxyl moiety andthus creates a negative charge on the oxygen atom of the former hydroxylmoiety. This oxygen atom is now open for substitution by a substitutionagent, such as a cationic agent, such as a quaternary ammonium compound,for example a quaternary amine.

Table 1 describes the temperature, pressure, and corresponding functionof each zone of the extruder.

TABLE 1 Temp. Description Zone (° F.) Pressure of Screw Purpose 1 70 LowFeeding/Conveying Feeding and Mixing 2 70 Low Conveying Mixing andConveying 3 70 Low Conveying Mixing and Conveying 4 130 LowPressure/Decreased Conveying and Heating Conveying 5 300 Medium PressureGenerating Cooking at Pressure and Temperature 6 250 High ReversingCooking at Pressure and Temperature 7 210 Low Conveying Cooling andConveying (with venting) 8 210 Low Pressure Generating ConveyingAfter the third hydroxyl polymer composition exits the extruder, part ofthe polymer composition can be dumped and another part (100 g) can befed into a Zenith®, type PEP II (Sanford N.C.) and pumped into a SMXstyle static mixer (Koch-Glitsch, Woodridge, Ill.). The static mixer isused to combine additional additives such as crosslinking agents,crosslinking facilitators, external plasticizers, such as water, withthe third hydroxyl polymer composition. The additives are pumped intothe static mixer via PREP 100 HPLC pumps (Chrom Tech, Apple ValleyMinn.). These pumps provide high pressure, low volume additioncapability. The third hydroxyl polymer composition of the presentinvention exhibits a Capillary Number of at least 1 and thus, is readyto be polymer processed into a hydroxyl polymer fiber.b. Polymer Processing the Polymer Composition into a Hydroxyl PolymerFiber

The hydroxyl polymer composition is then polymer processed into ahydroxyl polymer fiber. Nonlimiting examples of polymer processingoperations include extrusion, molding and/or fiber spinning. Extrusionand molding (either casting or blown), typically produce films, sheetsand various profile extrusions. Molding may include injection molding,blown molding and/or compression molding. Fiber spinning may includespun bonding, melt blowing, continuous fiber producing and/or tow fiberproducing. Fiber spinning may be dry spinning or wet spinning.Monocomponent fibers comprising the hydroxyl polymer composition areformed by the fiber spinning.

c. Forming Hydroxyl Polymer Fiber Fibrous Structure

Hydroxyl polymer fibers produced as a result of polymer processing ofthe polymer composition in accordance with the present invention may becombined into a fibrous structure by collecting a plurality of thefibers onto a belt or fabric.

A plurality of solid additives may be combined with the hydroxyl polymerfibers as the fibers are being deposited onto a collection device, suchas a belt or fabric.

In one example, a first gas stream may comprise a plurality of hydroxylpolymer fibers and a second gas stream may comprise a plurality of solidadditives. The two gas streams may be combined prior to and/orconcurrently with depositing the hydroxyl polymer fibers and solidadditives onto a collection device such that the solid additives areentrained within and/or on the resulting fibrous structure. An exampleof equipment suitable for use in this type of process are described inUS Patent Application 2003/0114067.

A fibrous structure of the present invention may then be post-processedby subjecting the web to a post-processing operation. Nonlimitingexamples of post processing operations include contacting the fibrousstructure with a plurality of solid additives, curing, embossing,thermal bonding, humidifying, perfing, calendering, printing,differential densifying, tuft deformation generation, and other knownpost-processing operations.

d. Contacting Surfaces of a Fibrous Structure with Solid Additives

Solid additives may be applied to a fibrous structure by any suitablemeans known in the art. When solid additives are applied to a fibrousstructure, a surface of the fibrous structure comprising the solidadditives is formed. A nonlimiting example by which solid additives maybe applied to the fibrous structure is by using a Dan Web former, anexample of which is described in U.S. Pat. No. 5,885,516, commerciallyavailable from Dan-Web of Risskov, Denmark.

Hydroxyl Polymer Fiber Fibrous Structure

As shown in FIG. 2, a hydroxyl polymer fiber fibrous structure 20comprises a hydroxyl polymer fiber 22 (a plurality of hydroxyl polymerfibers 22 may form a base substrate upon which solid additives may bedeposited) and a solid additive 24, which may be a particle and/or anaturally occurring fiber.

The hydroxyl polymer fiber fibrous structure 20 may comprise a firstsurface 26 and a second surface 28 opposite from the first surface 26 asshown in FIG. 3. The solid additive 24 may be present on a surface ofthe fibrous structure, such as the first surface 26. The solid additive24 may cover less than the entire surface area of the surface of thefibrous structure. The solid additive 24 may be present on the surfaceof the fibrous structure in a random pattern. The solid additive 24 maybe present on the surface of the fibrous structure in a non-randomrepeating pattern.

For explanation and/or clarity purposes, the solid additives 24 areshown in a dispersed nature, however, the concentration of the solidadditives 24 on the first surface 26 of the hydroxyl polymer fiberfibrous structure 20 and/or the second surface 28 of the hydroxylpolymer fiber fibrous structure 20 may be such that the entire surfacearea or almost the entire surface area of the first surface 26 and/orthe second surface 28 may be in contact with the solid additives 24.

As shown in FIGS. 4 and 5, in one example of the present invention, amulti-layered hydroxyl polymer fiber fibrous structure 30 comprises afirst layer 32 comprising a plurality of hydroxyl polymer fibers, asecond layer 34 comprising a plurality of solid additives, and a thirdlayer 36 comprising a plurality of hydroxyl polymer fibers.

In one example, the fibrous structure 30 may comprise at least one layercomprising a majority of non-naturally occurring hydroxyl polymer fibers22 and at least one layer comprising a majority of solid additives 24.

In another example, the solid additives 24 may be uniformly orsubstantially uniformly distributed throughout the fibrous structure.

In yet another example, the solid additives 24 may be non-uniformlydistributed throughout the fibrous structure.

FIG. 6 illustrates still another example of a hydroxyl polymer fiberfibrous structure of the present invention. The hydroxyl polymer fiberfibrous structure 20 comprises a hydroxyl polymer fiber 22 and aplurality of solid additives 24. As shown in FIG. 6, the plurality ofsolid additives 24 are arranged in a non-random, repeating pattern on asurface of the hydroxyl polymer fiber fibrous structure 20. Depositingthe solid additives in a non-random, repeating pattern can be achievedby any suitable means known in the art. For example, a patterned maskmay be placed on the hydroxyl polymer fiber fibrous structure such thatonly the open areas of the mask allow the solid additives to contact asurface of the hydroxyl polymer fiber fibrous structure.

FIG. 7 illustrates still yet another example of a hydroxyl polymer fiberfibrous structure of the present invention. The hydroxyl polymer fiberfibrous structure 20 comprises a hydroxyl polymer fiber 22 and aplurality of solid additives 24. As shown in FIG. 7, the plurality ofsolid additives 24 are arranged in a random pattern on a surface of thehydroxyl polymer fiber fibrous structure 20.

In one example, the hydroxyl polymer fiber fibrous structure of thepresent invention may comprise greater than 40% and/or greater than 45%and/or greater than 50% by bone dry weight of the hydroxyl polymerfibers.

In another example, the hydroxyl polymer fiber fibrous structure of thepresent invention may comprise less than 60% and/or less than 50% and/orless than 30% and/or less than 15% and/or less than 5% and/or less than2% by bone dry weight of the solid additives.

Test Methods

Unless otherwise indicated, all tests described herein including thosedescribed under the Definitions section and the following test methodsare conducted on samples that have been conditioned in a conditionedroom at a temperature of 73° F.±4° F. (about 23° C.±2.2° C.) and arelative humidity of 50%±10% for 24 hours prior to the test. Samplesconditioned as described herein are considered dry samples (such as “dryfibrous structures”) for purposes of this invention. Further, all testsare conducted in such conditioned room. Tested samples and felts shouldbe subjected to 73° F.±4° F. (about 23° C.±2.2° C.) and a relativehumidity of 50%±10% for 24 hours prior to testing.

A. Pore Volume Distribution Test Method

Pore Volume Distribution measurements are made on a TRI/Autoporosimeter(TRI/Princeton Inc. of Princeton, N.J.). The TRI/Autoporosimeter is anautomated computer-controlled instrument for measuring pore volumedistributions in porous materials (e.g., the volumes of different sizepores within the range from 1 to 900 μm effective pore radii).Complimentary Automated Instrument Software, Release 2000.1, and DataTreatment Software, Release 2000.1 is used to capture, analyze andoutput the data. More information on the TRI/Autoporosimeter, itsoperation and data treatments can be found in The Journal of Colloid andInterface Science 162 (1994), pgs 163-170, incorporated here byreference.

As used in this application, determining Pore Volume Distributioninvolves recording the increment of liquid that enters or leaves aporous material as the surrounding air pressure changes. A sample in thetest chamber is exposed to precisely controlled changes in air pressure.The size (radius) of the largest pore able to hold liquid is a functionof the air pressure. As the air pressure increases (decreases),different size pore groups drain (absorb) liquid. The pore volume ofeach group is equal to this amount of liquid, as measured by theinstrument at the corresponding pressure. The effective radius of a poreis related to the pressure differential by the following relationship.

Pressure differential=[(2)γ cos Θ]/effective radius

where γ=liquid surface tension, and Θ=contact angle.

Typically pores are thought of in terms such as voids, holes or conduitsin a porous material. It is important to note that this method uses theabove equation to calculate effective pore radii based on the constantsand equipment controlled pressures. The above equation assumes uniformcylindrical pores. Usually, the pores in natural and manufactured porousmaterials are not perfectly cylindrical, nor all uniform. Therefore, theeffective radii reported here may not equate exactly to measurements ofvoid dimensions obtained by other methods such as microscopy. However,these measurements do provide an accepted means to characterize relativedifferences in void structure between materials.

The equipment operates by changing the test chamber air pressure inuser-specified increments, either by decreasing pressure (increasingpore size) to absorb liquid, or increasing pressure (decreasing poresize) to drain liquid. The liquid volume absorbed (drained) at eachpressure increment is the cumulative volume for the group of all poresbetween the preceding pressure setting and the current setting.

In this application of the TRI/Autoporosimeter, the liquid is a 0.2weight % solution of octylphenoxy polyethoxy ethanol (Triton X-100 fromUnion Carbide Chemical and Plastics Co. of Danbury, Conn.) in distilledwater. The instrument calculation constants are as follows: p(density)=1 g/cm³; γ (surface tension)=31 dynes/cm; cos Θ=1. A 0.22 μmMillipore Glass Filter (Millipore Corporation of Bedford, Mass.; Catalog# GSWP09025) is employed on the test chamber's porous plate. Aplexiglass plate weighing about 24 g (supplied with the instrument) isplaced on the sample to ensure the sample rests flat on the MilliporeFilter. No additional weight is placed on the sample. The remaining userspecified inputs are described below. The sequence of pore sizes(pressures) for this application is as follows (effective pore radius inμm): 1, 2.5, 5, 10, 15, 20, 30, 40, 50, 60, 70, 80, 90, 100, 120, 140,160, 180, 200, 225, 250, 275, 300, 350, 400, 450, 500, 600, 700, 800,900, 800, 700, 600, 500, 450, 400, 350, 300, 275, 250, 225, 200, 180,160, 140, 120, 100, 90, 80, 70, 60, 50, 40, 30, 20, 15, 10, 5, 2.5, 1,2.5, 5, 10, 15, 20, 30, 40, 50, 60, 70, 80, 90, 100, 120, 140, 160, 180,200, 225, 250, 275, 300, 350, 400, 450, 500, 600, 700, 800, 900. Thissequence starts with the sample dry, saturates it as the pore settingsincrease (1^(st) absorption), and then subsequently drains the sample ofall volume above an effective pore radius of 1.0 μm (desorption), andthen finally saturates it again as the pore settings increase a secondtime (2^(nd) absorption). The equilibrium rate is set at 5 mg/minute. Nostop radius is specified.

In addition to the test materials, a blank condition (no sample betweenplexiglass plate and Millipore Filter) is run to account for any surfaceand/or edge effects within the chamber. Any pore volume measured forthis blank run is subtracted from the applicable pore grouping of thetest sample. This data treatment can be accomplished manually or withthe available TRI/Autoporosimeter Data Treatment Software, Release2000.1.

In regards to wet fibrous structure (web) collapse, the characteristicpore size distribution of the 2^(nd) absorption portion of the testingsequence is analyzed, since absorption in the 1^(st) absorption portionof the testing sequence can sometimes vary based on how the dry fibrousstructure contacts the wetted filter (influenced by dry fibrousstructure texture, embossing, etc.). Thus, after the desorption portionof the testing sequence, the sample, already wetted once, is expected tobe in better hydraulic contact with the porous filter (due to lowerfiber and fibrous structure (web) modulus when wet).

The TRI/Autoporosimeter reports the weight (mg) of liquidabsorbed/desorbed from each pore group as chamber pressure is stepchanged according to the prescribed testing sequence. From this data,the liquid density, and the weight of the original, dry sample, theratio of pore volume/sample weight can be calculated. This value can bereported as mm³/mg of dry sample mass. Similarly, the pore volume/drysample weight over a specified pore size range (e.g., 20-500 μm) can becalculated by simply summing the reported pore volumes of each poresetting included in that range and dividing by the dry sample mass.These data treatments are conducted manually based on the output of theAutomated Instrument Software, Release 2000.1.

B. Fiber Diameter Test Method

A fibrous structure comprising hydroxyl polymer fibers of appropriatebasis weight (approximately 5 to 20 grams/square meter) is cut into arectangular shape, approximately 20 mm by 35 mm. The sample is thencoated using a SEM sputter coater (EMS Inc, PA, USA) with gold so as tomake the fibers relatively opaque. Typical coating thickness is between50 and 250 nm. The sample is then mounted between two standardmicroscope slides and compressed together using small binder clips. Thesample is imaged using a 10× objective on an Olympus BHS microscope withthe microscope light-collimating lens moved as far from the objectivelens as possible. Images are captured using a Nikon D1 digital camera. AGlass microscope micrometer is used to calibrate the spatial distancesof the images. The approximate resolution of the images is 1 μm/pixel.Images will typically show a distinct bimodal distribution in theintensity histogram corresponding to the fibers and the background.Camera adjustments or different basis weights are used to achieve anacceptable bimodal distribution. Typically 10 images per sample aretaken and the image analysis results averaged.

The images are analyzed in a similar manner to that described by B.Pourdeyhimi, R. and R. Dent in “Measuring fiber diameter distribution innonwovens” (Textile Res. J. 69(4) 233-236, 1999). Digital images areanalyzed by computer using the MATLAB (Version. 6.3) and the MATLABImage Processing Tool Box (Version 3.) The image is first converted intoa grayscale. The image is then binarized into black and white pixelsusing a threshold value that minimizes the intraclass variance of thethresholded black and white pixels. Once the image has been binarized,the image is skeletonized to locate the center of each fiber in theimage. The distance transform of the binarized image is also computed.The scalar product of the skeltonized image and the distance mapprovides an image whose pixel intensity is either zero or the radius ofthe fiber at that location. Pixels within one radius of the junctionbetween two overlapping fibers are not counted if the distance theyrepresent is smaller than the radius of the junction. The remainingpixels are then used to compute a length-weighted histogram of fiberdiameters contained in the image.

All documents cited in the Detailed Description of the Invention are, inrelevant part, incorporated herein by reference; the citation of anydocument is not to be construed as an admission that it is prior artwith respect to the present invention.

The dimensions and values disclosed herein are not to be understood asbeing strictly limited to the exact numerical values recited. Instead,unless otherwise specified, each such dimension is intended to mean boththe recited value and a functionally equivalent range surrounding thatvalue. For example, a dimension disclosed as “40 mm” is intended to mean“about 40 mm”.

While particular embodiments/examples of the present invention have beenillustrated and described, it would be obvious to those skilled in theart that various other changes and modifications can be made withoutdeparting from the spirit and scope of the invention. It is thereforeintended to cover in the appended claims all such changes andmodifications that are within the scope of this invention.

What is claimed is:
 1. A fibrous structure comprising a plurality ofmonocomponent, non-naturally occurring polysaccharide fibers and aplurality of solid additives.
 2. The fibrous structure according toclaim 1 wherein the fibrous structure exhibits a total pore volume ofpores in the range of greater than 20 μm to 500 μm of greater than 3.75mm³/mg of dry fibrous structure mass.
 3. The fibrous structure accordingto claim 1 wherein the solid additives are present on at least onesurface of the fibrous structure.
 4. The fibrous structure according toclaim 3 wherein the solid additives cover less than the entire surfacearea of the surface of the fibrous structure.
 5. The fibrous structureaccording to claim 3 wherein the solid additives are present on thesurface of the fibrous structure in a random pattern.
 6. The fibrousstructure according to claim 3 wherein the solid additives are presenton the surface of the fibrous structure in a non-random repeatingpattern.
 7. The fibrous structure according to claim 1 wherein the solidadditives are uniformly distributed throughout the fibrous structure 8.The fibrous structure according to claim 1 wherein the solid additivesare non-uniformly distributed throughout the fibrous structure.
 9. Thefibrous structure according to claim 1 wherein at least one of the solidadditives exhibits a critical surface tension of greater than about 30dynes/cm.
 10. The fibrous structure according to claim 1 wherein thesolid additives are selected from the group consisting of: hydrophilicinorganic particles, hydrophilic organic particles, hydrophobicinorganic particles, hydrophobic organic particles, naturally occurringfibers, non-naturally occurring particles, other non-naturally occurringfibers and mixtures thereof.
 11. The fibrous structure according toclaim 10 wherein the naturally occurring fibers comprise a wood pulpfiber.
 12. The fibrous structure according to claim 10 wherein thenaturally occurring fibers comprise a cotton linter.
 13. The fibrousstructure according to claim 10 wherein the naturally occurring fiberscomprise protein.
 14. The fibrous structure according to claim 10wherein the other non-naturally occurring fibers are selected from thegroup consisting of: polyolefin fibers, polyamide fibers and mixturesthereof.
 15. The fibrous structure according to claim 10 wherein thehydrophilic inorganic particles are selected from the group consistingof: clay, calcium carbonate, titanium dioxide, talc, aluminum silicate,calcium silicate, alumina trihydrate, activated carbon, calcium sulfate,glass microspheres, diatomaceous earth and mixtures thereof.
 16. Thefibrous structure according to claim 1 wherein the fibrous structurecomprises at least one layer comprising a majority of non-naturallyoccurring polysaccharide fibers and at least one layer comprising amajority of solid additives.
 17. The fibrous structure according toclaim 1 wherein the non-naturally occurring polysaccharide fibercomprises a polysaccharide selected from the group consisting of:starch, starch derivatives, starch copolymers, chitosan, chitosanderivatives, chitosan copolymers, cellulose, cellulose derivatives,cellulose copolymers, gums, arabinans, galactans, and mixtures thereof.18. The fibrous structure according to claim 17 wherein thenon-naturally occurring polysaccharide fiber further comprises ahydroxyl polymer selected from the group consisting of: polyvinylalcohol, polyvinyl alcohol derivatives, polyvinyl alcohol copolymers,proteins, and mixtures thereof.
 19. The fibrous structure according toclaim 1 wherein at least one of the solid additives exhibits a particlesize of less than 6 mm in the maximum dimension.
 20. The fibrousstructure according to claim 1 wherein the fibrous structure comprisesless than 50% by bone dry weight of the solid additives.
 21. A single-or multi-ply sanitary tissue product comprising a fibrous structureaccording to claim
 1. 22. A fibrous structure comprising monocomponent,non-naturally occurring hydroxyl polymer fibers and solid additives,wherein the non-naturally occurring hydroxyl polymer fibers are presentat a greater bone dry weight than the solid additives.
 23. A fibrousstructure comprising a plurality of monocomponent, non-naturallyoccurring hydroxyl polymer fibers and a pore volume enhancing systemthat increases the total pore volume of pores in the range of greaterthan 20 μm to 500 μm of the fibrous structure compared to the samefibrous structure without the pore volume enhancing system.
 24. Afibrous structure comprising a monocomponent, non-naturally occurringhydroxyl polymer fiber wherein the fibrous structure exhibits a totalpore volume of pores in the range of greater than 20 μm to 500 μm ofgreater than 3.75 mm³/mg of dry fibrous structure mass.